New water-soluble highly selective fluorescent chemosensor for Fe (III) ions and its application to living cell imaging

A new rhodamine-based chemosensor exhibits excellent selectivity for Fe3+ ions over a wide range of tested metal ions Ag+, Al3+, Ca2+, Cd2+, Co2+, Cr3+, Cu2+, Fe2+, Hg2+, Mg2+, Mn2+, Ni2+, Pb2+, and Zn2+ in an aqueous solution. The binding of Fe3+ to chemosensor 1 produces an absorption band at 564 nm and an emission band at 588 nm because Fe3+-binding induces ring-opening of the spirolactam in 1. The binding ratio of the 1–Fe3+ complexes was determined to be 1:1 according to a Job plot. The association constant (Ka) of Fe3+ binding in chemosensor 1 was 6.9 × 103 M−1. The maximum fluorescence enhancement caused by Fe3+ binding in chemosensor 1 occurred at a pH range of 6–7.5. The fluorescence microscopy experiments in this study demonstrated that chemosensor 1 can be used as a fluorescent probe for detecting Fe3+ in living cells.